For the landing of aircraft, a number of well known automatic guidance systems have been implemented. The automatic guidance of an aircraft involves accurately determining the current position of the aircraft in order to automatically correct, if necessary, its trajectory to align it correctly with a landing runway for example. This determination of the current position of the aircraft can be performed using different systems.
Among these systems, the best known are the ILS (instrument landing system) systems. The ILS systems are instrument approach systems for aircraft that are equipped therewith. The ILS system makes it possible to indicate to the pilot the manoeuvres to be performed to achieve a successful landing. These systems therefore require specific instrumentation onboard the aircraft and detection and guidance systems on the ground.
Another guidance system employed at airports is the MLS (Microwave Landing System). The MLS is a microwave landing system. It makes it possible to provide accurate guidance for a landing, regardless of the weather conditions.
The ILS and MLS systems are very heavy equipment, both on the ground and onboard the aircraft. Also, it is not possible to envisage installing such equipment on a small platform such as a ship. Furthermore, light aircraft cannot incorporate the equipment needed to implement these systems, as much for reasons of cost as for lack of space.
Apart from these conventional means that are mainly used by commercial civil aviation, other solutions can be envisaged.
A first solution uses a satellite positioning system, this type of system being commonly designated by the acronym GNSS (Global Navigation Satellite System). Among these positioning systems, the GPS (Global Positioning System) system is, these days, the most widely used. The main drawback of the GNSS systems is their lack of robustness. In practice, this type of service is not always available and is sensitive to electromagnetic disturbances.
A second solution is to use a LIDAR (Light Detection And Ranging) system. This locating system, which operates on the same principle as radars, uses lasers in the visible range, or even in the infrared range. This therefore renders it inoperative when the weather conditions are unfavourable.
Another solution consists in using a highly directional millimetric wave radar. The millimetric wave radar also requires a search phase to designate the target. It must also be positioned accurately relative to the landing runway. This solution is also very costly and often requires a transponder onboard the aircraft. The transponder is itself costly, bulky, heavy, and consumes a lot of energy. It is also essential to make it redundant for dependability reasons.
Other locating methods that facilitate the automatic guidance of the aircraft have been proposed in the past. Notable among these are the international patent applications referenced under the respective numbers WO2006/053868, WO2007/063126, which notably use a radar and a multifunction beacon onboard the aircraft.
However, the latter methods are similarly difficult to apply in the case of a decking on a mobile platform such as a ship or an oil platform, especially when the environmental conditions are unfavourable. For example, in the case of a rough sea, the aircraft may have to land on a surface that is subject to strong roll, pitch, heave, surge and/or sway movements, making the decking operation difficult, or even hazardous. Furthermore, the structure of the platform can cause turbulent winds to appear around the aircraft.
Furthermore, the solutions that employ a conventional radar require a transmission of a signal from the platform that is of sufficiently high power to receive the skin echo from the aircraft. These solutions are incompatible with the constraints of electromagnetic compatibility and possible electromagnetic discretion requirements.
Guidance techniques that use optical sensors such as infrared or optical, thermal or laser cameras can also be implemented. However, these techniques are not compatible when the aim is to be able to perform a decking regardless of the visibility conditions, and notably in misty weather.
Moreover, although the international patent applications referenced under the numbers WO2007/131923 and WO2008/113750 address the problem of multiple paths of waves deriving from reflections on the decking surface which, for example, is a ship's metal deck, the presence of side walls reflecting the electromagnetic waves in proximity to the decking area can lead to the appearance of other multiple paths of waves that can also disrupt the measurements. Now, on ships for example, the presence of such walls is possible.